This invention relates to the field of commercial cookery, and more particularly to comestible kettles wherein comestibles are cooked by floating in a heated fluid such as shortening. Typically a kettle of this sort is a shallow container of considerable size, containing the cooking fluid, and crossed at intervals by heaters in the form of tubes which remain below the surface of the fluid. Each heater has a flame directed into one of its ends by a suitable burner which supplies both the fuel and the air necessary for combustion, the other end of the heater being connected to an exhaust header or flue. Comestibles are placed in the fluid at one end of the kettle and are removed at the other end after cooking.
When it is attempted to increase the production of comestibles by a kettle such as this, the only variable available to the designer is the area of the fluid on which the comestibles float while frying. An attempt to increase this area by lengthening the kettle quickly reached a limitation in that the interval of contact with the hot fluid cannot be extended without injury to the quality of the product so that the comestibles had therefore to move through the longer kettle more rapidly; a condition was reached in which it became physically impossible to perform rapidly enough the necessary process of turning the comestibles over to cook the second side.
Difficulty has also been experienced in attempting to increase the cooking area by widening the kettle. Experience has shown that a considerable thermal gradient exists across such a heater, the end nearer the burner being considerably hotter than the flue end. This results in product color variation, the comestibles moving along the side of the kettle where the burners are located being darker than those on the other side of the kettle. It also results in convection currents in the fluid which cause the products to crowd together toward the colder side of the kettle. Finally it results in rapid breakdown of the cooking fluid by reason of contact with high temperature heater tube ends.
An attempt to overcome these effects by including a spiral metal baffle within the heater tube for a considerable portion of its length extending from the flue end, as suggested in FIG. 3, has not met with success. SUMMARY OF THE INVENTION
I have discovered that it is possible to reduce the proportion of heat transmitted to the fluid at the burner end of the heater tube, and simultaneously increase the proportion at the flue end of the tube. This decreases the thermal gradient along the heater tube to a point where the effects itemized above are reduced to tolerable levels. I accomplish it by inserting a shroud tube into the heater tube at the burner end, and an axial baffle tube into the heater tube at the flue end. The shroud tube is perforated and when the flame is directed into it at least part of the flame heat is converted to radiant heat which is more uniform and less intense. The baffle tube is conical for at least a portion of its length, its smallest diameter being furthest from the flue end and being closed. Hot gases from the flame are thus displaced ever closer to the inner surface of the heater tube, and move with ever greater velocity. Both of these effects lead to greater heat transfer toward the flue end of the heater tube.
A principle object of the invention is accordingly to provide an improved comestible kettle including an improved heater therefor. Another object of the invention is to provide a comestible kettle heater along which the thermal gradient is small. Another object is to provide such a heater with means at its burner end for decreasing the proportion of the heat transmitted to the fluid. Another object is to provide such a heater with means at the flue end thereof for increasing the proportion of heat transmitted to the fluid. Another object of the invention is to provide a method for increasing the uniformity of heat transfer to a fluid along the length of a heater tube. A more specific object of the invention is to provide a heater with an internal shroud tube at its burner end and an internal tapering baffle tube at its flue end, which function to reduce the thermal gradient along the tube.
Various other objects, advantages, and features of novelty which characterize my invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. However, for a better understanding of the invention, its advantages, and objects attained by its use, reference should be had to the drawing which forms a further part hereof, and to the accompanying descriptive matter, in which there is illustrated and described a preferred embodiment of the invention.